1. Technical Field of the Invention
The present invention relates to a method and apparatus for evaluating the progress of osteoporosis by utilizing ultrasonic signals.
2. Description of Related Art
With an increase in population of aged people, there is a rapid increase in number of patients who suffer from a disease called osteoporosis, which causes fractures of bones, and it is becoming a great concern in the medical field. With a decrease in the calcium content in a bone structure, cracking and damage of bones are easily caused by deterioration in the strength of bone. About 30% of women and about 10% of men who are more than 60 years old are said to be suffering from osteoporosis. If a symptom of osteoporosis is discovered at an early stage, it may be possible to effectively prevent the progress of the disease with a variety of medical treatments. It is, therefore, very important to undergo a medical examination at regular intervals in order to detect the disease in its early stages. Heretofore, it has been practiced to preestimate the degree of progress of the osteoporosis by measuring bone mineral content (BMC) by roentgen irradiation (D-ray) or by gamma radiation.
However, the radiation is very harmful to the living body, and people ranging from about 50 to over 60 years old who might have osteoporosis and post-menopausal women have had to undergo such a hazardous medical examination by the use of radiation. In order to avoid such a hazardous treatment, there have been proposed apparatuses for evaluating osteoporosis by utilizing ultrasonic signals which are not harmful to the human body.
For example, there have been proposed some apparatuses wherein an ultrasonic signal is transmitted to a patient to determine a velocity of sound and attenuation in a bone structure from a signal received, and the data received are used as indicators for evaluation of the disease (for example JP-A-1-503199, JP-A-2-104337, and JP-A-4-501519).
As shown in FIG. 17 of the accompanying drawings, an indicator of `stiffness` which is computerized from information obtained by transmission of an ultrasonic signal is plotted on the vertical axis, and `age` is plotted along the horizontal axis to draw a graph of the data of an average healthy person. Then, an indication is made, by plotting the data thereon, to show how different a patient (person being examined) is from a healthy person, and a determination is made whether the patient is under normal condition or the patient requires immediate medical treatment.
From the standpoint of a patient, the patient may understand how far his condition is from an image displayed comparing with a standard curved line of a healthy person. However, the patient hardly obtains a satisfactory explanation how it relates to the progress of osteoporosis and how the condition of the disease is progressing even if he asks for an explanation from doctors and nurses.